1. Technical Field
The present invention concerns an electromagnetic driven membrane pump. More specifically, the invention relates to an electromagnetic driven membrane pump in accordance with the claims.
2. Technical Background
Membrane pumps that apply pressure or negative pressure are found in a large variety of variations and sizes and are used in many different applications, everything from large industrial membrane pumps to very small membrane pumps for medical purposes. A significant problem during the development of small membrane pumps is that it is difficult to construct a membrane pump that combines a cost efficient method of production with a long lifespan and a high performance level.
The most common type of membrane pump that exists is driven by a rotating motor, which with the aid of an eccentric causes a membrane to perform an oscillating pumping motion. An advantage of powering a membrane pump with an electric motor is that the diameter of the rotor can be chosen to create an adequate lever in order to accomplish the needed moment to perform the pumping, oscillating motion. By adjusting the length of the lever it is possible to choose the gear changing of the motor's output to coincide with the pressure that the membrane pump produces, so that for example high pressure can be attained with minimal motor output. Another advantage with this type of membrane pump is that the membrane attains a well defined end point of the pump stroke.
The main disadvantage with powering a membrane pump with a rotating motor is the life span of the pump is to a large degree dependant on which type of motor that is used. Essential for the life span and efficiency of the membrane pump is the way in which the motor in the membrane pump is journalled in bearings and if the motor is brushless and the like. The life span of the membrane pump depends to a lesser degree upon the membrane or other parts of the pump. This results in that the cost of a motor for a membrane pump with a long life span becomes a significant part of the total cost of the membrane pump. It is easy to understand why the motor is a significant part of the cost, when motors with long life spans are mechanically and electronically advanced to manufacture with many accompanying details. This problem is also described in patent document U.S. Pat. No. 6,589,028 where a similar discussion is presented for these types of pumps.
For quite some time it has been known that a membrane pump may be driven with the aid of one or more electromagnets. An electromagnet produces a back and forth movement that causes the membrane to produce a pumping movement. Powering a membrane pump with an electromagnet instead of a rotating motor can at first glance seem as a better solution. An advantage with electromagnetic driven membrane pumps is that they are more closely coupled to the membrane which renders it possible to have greater control over length of stroke, frequency and speed in the actual pump housing compared to membrane pumps powered by rotating motors.
Electromagnetic pumps are still less common despite that they logically should be cheaper to manufacture and are more easily controlled than pumps powered by rotating motors. This is caused by several problems that together result in the fact that an electromagnet is not obviously better at powering a membrane pump compared with a rotating motor. A significant problem with electromagnetic driven pumps is that they are difficult to gear up without the magnetically driven body losing its straight linear movement. This often also results in creating additional points of friction that are expensive to mount in bearings.
Additional problems with existing electromagnetic driven membrane pumps consist of suspension mounting and bearing support of the moving part that drives the membrane, comprised of a magnet or a magnetic conducting body. For an electromagnetic driven membrane pump to attain a long life span as well as being as efficient as possible, it is paramount that the moving parts have as low a friction as possible, preferably no friction at all. In order to maximize the life span of the membrane pump, it is furthermore important to counteract the rotation in the coupling between the membrane and the moving part (axle or the like). In order to maximize the life span of the membrane, it is furthermore important to counteract the transverse loads that can reduce the life span of the membrane as well as counteracting the membrane stretching so much that it strikes the turning position. It is also of great importance that the membrane has a well defined neutral point when the pump is in its rest position so equality in performance is attained during multiple productions.
The above mentioned problems with pumps based on electromagnets gives rise to very intricate designs comprised of many details making production very costly. An example of such a design is for example described in patent document U.S. Pat. No. 5,360,323. This patented design is very different from the present invention.